As operational frequencies of microwave components and subsystems have increased, performance of electrical feed-through connections between microwave integrated circuits and coaxial connectors, waveguides, etc., has become critical. With the advent of multi-function monolithic microwave integrated circuit (MMIC) chips, impedance matching and hermeticity—not normally required at lower frequencies—have become important and tightly toleranced design criteria.
Hermeticity in microwave packages is commonly achieved by use of one or more dielectric inserts or beads. The dielectric inserts themselves are hermetic and can either be molded or fired into a sleeve, which is then soldered into a package. If the sleeve is correctly soldered into the package, the package can be hermetically sealed. Alternatively, a dielectric insert can be molded or fired directly into the package to reduce manufacturing cost while providing greater reliability.
For high frequency microwave applications, features surrounding the dielectric insert are critical for good RF performance and such features must be tightly toleranced during manufacturing. For MMICs, coaxial connector assembly components provide electrical transition and impedance matching between a coaxial transmission line of a coaxial connector and a microstrip transmission line connected to the MMICs. To achieve impedance matching, connector components include impedance compensation. Impedance compensation can include, for example, an air dielectric between the microstrip and a coaxial connector housing, and an additional compensation gap between the dielectric insert and the air dielectric. Integrating a dielectric insert into a package and forming an air dielectric and compensation gap between the dielectric insert and a package housing becomes more difficult as components shrink in size and tolerances of features tighten.